The present invention relates to a sintered plain bearing, for motors and gear drives having a running surface formed by a bearing bore and capable of having lubricant applied to it from lubricant reservoirs in the bearing, in which the bearing bore has, alternatingly distributed over the circumference, high-compaction small-pore running surfaces and axially extending low-compaction open-pore lubricant reservoirs.
A sintered plain bearing of this kind is described in the German periodical Tribologie+Schmierungstechnik, Vol. 45, 1/1998, pages 47-48. The lubricant reservoirs are introduced into the bearing bore of the sintered element as grooves that are triangular in section, while the running surfaces between the grooves are compacted by sizing. These lubricant reservoirs can readily receive lubricant that is displaced during operation from the sintered bearing, i.e. from the regions thereof that are not highly compacted, but they cannot, especially during the initial phases of operation, make a significant contribution to lubrication of the running surfaces of the bearing bore and the shaft sliding thereon.
The same is also analogously true of a sintered plain bearing as defined in U.S. Pat. No. 5,704,718, in which the lubricant reservoirs form large U-shaped grooves whose groove bottoms are stepped back from the running surfaces with a greater diameter. The lubricant accumulated in these grooves in the stationary state cannot effectively contribute to lubrication during the initial phases of operation. The lubricant reservoirs must first fill up with lubricant in order for effective lubrication of the shaft in the bearing bore to be achieved.
It is the object of the present invention, in the context of a sintered plain bearing of the kind mentioned initially, to improve lubrication especially in the initial phases of operation, without impairing the lubrication accomplished during operation by the lubricant that has passed into the lubricating oil reservoirs.
This object is achieved, according to the present invention, in that the lubricant reservoirs are constituted by channel structures having at least two longitudinal channels; and that at least in some of the channel structures, some of the channel crests remaining between adjacent longitudinal channels are in contact with the shaft received by the bearing bore in order to transfer lubricant.
Once lubricant has been taken up again, after operation, from the low-compaction region of the channel structures, i.e. once the longitudinal channels of the channel structures are lubricant-free, then at least some channel crests still remain in contact with the shaft for lubricant transfer, so that lubrication of the shaft is already occurring in the initial phase of a subsequent operating period, and then transitions into operating lubrication from the longitudinal channels.
The channel structures, introduced during pressing of the green compact, are not further compacted during sizing and therefore still have open pores, so that their storage capacity remains independent of the strength of the running surfaces.
For lubricant circulation, the configuration of the channel structures is preferably such that the width of the longitudinal channels, configured as capillary channels, is at least 20 times smaller than the height to which the lubricant being used rises in a glass capillary having a diameter of 1 mm.
The groove bottoms of the longitudinal channels, and the channel crests, are rounded and have a radius that is at least twice as small as the width of the longitudinal channels.
Since the channel crests between adjacent longitudinal channels are in contact with the shaft only for lubricant transfer thereto, they participate in non-load-bearing fashion. Their low load-bearing capacity resulting from their open pores and lower compaction has no negative repercussions on the service life of the sintered plain bearing.
In a cross-sectional plane perpendicular to a longitudinal axis of the bearing, the longitudinal channels define respective V-shapes that widen toward the shaft with an opening angle that is less than 12xc2x0.
According to a development, the lubricant storage capacity can be increased even further by the fact that additional open-pore lubricant reservoirs, shaped like channels or blind holes and adapted in terms of opening angle, width, and radius of the channel bottom to the corresponding dimensions of the longitudinal channels, are introduced into the end faces and/or the outer surface.
The open-pore lubricant reservoirs of the end faces can be configured as concentric channel rings and/or channel ring segments which are guided via radial channels to the running surface of the sintered plain bearing. The channel ring segments are longer than 0.2 mm.
Radial channels, which extend from the outer surface to the running surface of the sintered plain bearing, can also be introduced in a manner uniformly distributed over the end faces.
According to one embodiment provision is made in the context of the open-pore lubricant reservoirs in the outer surface for circumferential channels and/or circumferential channel segments and/or blind holes to be introduced into the outer surface as lubricant reservoirs. The circumferential channels and/or circumferential channel segments can be connected to one another via transversely extending connecting channels. Provision is also made, in terms of the design of all the lubricant reservoirs, for the depth of the longitudinal channels, the radial channels, the channel rings and/or channel ring segments, and the circumferential channels and/or circumferential channel segments to be less than half the height to which the lubricant rises in a glass capillary having a diameter of 1 mm.